Various fuel delivery systems may be used to provide a desired amount of fuel to an engine for combustion. One type of fuel delivery system includes a port fuel injector for each cylinder of the engine to deliver fuel to respective cylinders. Still another type of fuel delivery system includes a direct fuel injector for each cylinder of the engine to deliver fuel directly to respective cylinders.
Engines have been described that utilize multiple fuel injector locations for each cylinder to deliver different types of fuel. One example is described in the papers titled “Calculations of Knock Suppression in Highly Turbocharged Gasoline/Ethanol Engines Using Direct Ethanol Injection” and “Direct Injection Ethanol Boosted Gasoline Engine: Biofuel Leveraging for Cost Effective Reduction of Oil Dependence and CO2 Emissions” by Heywood et al. Specifically, the Heywood et al. papers describe directly injecting ethanol into the cylinders to improve charge cooling effects, while relying on port injected gasoline for providing the majority of the combusted fuel over a drive cycle.
However, the inventor herein has recognized several issues with such systems. As one example, one of the gasoline or ethanol fuels may be used up by the engine before the other fuel, thereby potentially changing the performance characteristics of the engine. For example, if the ethanol as a knock suppressing fuel is exhausted before the gasoline, the occurrence or intensity of engine knock may increase, or the direct fuel injectors coupled with the ethanol fuel storage tank may over heat as a result of its reduced or discontinued delivery of the ethanol fuel to the engine. Furthermore, the inventor has also recognized that if a substitute fuel is provided to one of the fuel tanks to increase the amount of fuel available to the engine, a subsequent refueling operation of a more desirable fuel (e.g. a knock suppressant fuel) may not be realized where the substitute fuel still resides in the fuel tank.
To address these and other issues, the inventor herein has provided a fuel delivery system for an internal combustion engine and a method of operating the fuel delivery system. An example embodiment of the method includes: transferring at least some fuel from a first fuel storage region to a second fuel storage region via a pump during a first condition; draining at least some fuel from the second fuel storage region to the first storage fuel region via gravity during a second condition; and delivering fuel from the first fuel storage region to a first fuel injector of a cylinder of the internal combustion engine; and delivering fuel from the second fuel storage region to a second fuel injector of the cylinder. For example, the second fuel storage region may be arranged at a higher elevation relative to first fuel storage region.
In this way, a suitable amount of fuel may be maintained in the second fuel storage region by the fuel pump while fuel may be selectively provided to an engine cylinder via at least two different fuel injectors from each of the two fuel storage regions. In some examples, the first fuel injector may be configured as a port fuel injector and the second fuel injector may be configured as a direct fuel injector. By maintaining fuel in the second fuel storage region that supplies fuel to the direct fuel injector, injector overheating may be reduced while also providing sufficient charge cooling to reduce or eliminate engine knock. Yet, where a refueling operation of the second fuel storage region is to be performed, at least some of the previously transferred fuel may be returned to the first fuel storage region by draining the fuel with the assistance of gravity.